JERUSALEM – Israel hardened its insistence Monday that it would do anything it felt necessary to stop Iran from getting a nuclear bomb, just the ultimatum the United States hoped not to hear as it tried to nudge Iran to the bargaining table.

U.S. Defense Secretary Robert Gates reassured Israel that the new Obama administration was not naive about Iran’s intentions, and that Washington would press for new, tougher sanctions against the Iranians if they balk. He didn’t say what those might include.

Israeli Defense Minister Ehud Barak used a brief news conference with Gates to insist three times that Israel would not rule out any response — an implied warning that it would consider a pre-emptive strike to thwart Iran from obtaining nuclear weapons.

“We clearly believe that no option should be removed from the table,” Barak said. “This is our policy. We mean it. We recommend to others to take the same position, but we cannot dictate it to anyone.”

The question of how to deal with Iran’s rapid nuclear advancement has become a notable public difference between the new administrations in Jerusalem and Washington, despite overall close relations. Israel considers itself the prime target of any eventual Iranian bomb.

Iran says it is merely trying to develop nuclear reactors for domestic power generation. Israeli leaders fear the U.S. prizes its outreach to Iran over its historic ties to Israel and appears resigned to the idea that Iran will soon be able to build a nuclear weapon.

Obama says he has accepted no such thing. Still, the United States argues that an Israeli attack against Iran would upset the fragile security balance in the Middle East, perhaps triggering a new nuclear arms race and leaving everyone, including Israel and Iran, worse off.

Gates emphasized areas of agreement with Israel, including that the offer of talks with Iran must not be open-ended.

Later, in neighboring Jordan, Gates was blunt in describing what Iran might expect if it refuses the offer of international arms control talks this year, or walks away from Obama’s wider offer of better relations with Washington.

“If the engagement process is not successful, the United States is prepared to press for significant additional sanctions,” Gates said. He added that the U.S. would try to abandon the current policy of gradual international pressure, where layers of generally mild sanctions have been added each time Iran has flouted international demands.

“We would try to get international support for a much tougher position,” Gates said.

“Our hope remains that Iran would respond to the president’s outstretched hand in a positive and constructive way, but we’ll see.”

Gates’ brief stop in Israel was part of a parade of top Washington officials visiting Israel this week, with Iran and the expansion of Jewish settlements on Arab land the main topics. In each case, the Obama administration is taking a harder line with Israel than the positions taken by President George W. Bush.

Obama’s special Mideast envoy, former Sen. George Mitchell, was the first U.S. official to arrive, largely to discuss U.S.-Israeli differences over the settlements. Gates will be followed Wednesday by National Security Adviser James Jones and his deputy, Mideast and Iran specialist Dennis Ross, both expected to press for Israeli cooperation on Iran. Gates met with JordanianKing Abdullah II in Amman after leaving Israel on Monday.

Mitchell urged Israel to start “dealing with difficult issues like settlements.” At the same time, he urged Arab nations to take “genuine steps” toward normalizing ties with Israel.

The differences over Iran come on top of U.S.-Israeli disagreements over the Mideast peace process — particularly Washington’s calls for a halt to Israeli settlement building. The Obama administration is having to press Israel on multiple fronts at once, complicating its diplomacy as it makes a major push to revive Arab-Israeli negotiations.

All this comes at a time when Washington’s policy of dialogue with Iran itself has hit an impasse because of that country’s election turmoil.

A more cooperative Iran is important for the Mideast peace drive. With its links to Hamas and Hezbollah militants, Iran is capable of heightening tensions in Israel and the Palestinian territories. At the same time, an Israeli strike on Iran would probably push Arab nations away from any peace gestures toward Israel, despite their own rivalries with Tehran.

Israeli Prime Minister Benjamin Netanyahu “reiterated the seriousness (with) which Israel views Iran’s nuclear ambitions and the need to utilize all available means to prevent Iran from achieving a nuclear weapons capability,” Netanyahu’s office said following his meeting with Gates.

While the United States also reserves the right to use force if need be, the Obama administration is playing down that possibility while it tries to draw Iran into talks. Gates said Washington still hopes to have an initial answer in the fall about negotiations.

“The timetable the president laid out still seems to be viable and does not significantly raise the risks to anybody,” Gates said in Israel.

Both Barak and Gates said time is short. Other officials have said Iran is perhaps one to three years away from being able to build a nuclear weapon.

Barak, speaking in both English and Hebrew, gave only lukewarm endorsement to the negotiating strategy.

“We are not in a situation in which we can tell the United States to hold, or not to hold discussions with Iran,” Barak said. “But we repeatedly state our position in closed conversations, which is that a discussion like this should be limited in time, result-oriented, and able to decide if the Iranians are truly serious or not.”

Itamar Rabinovich, a former Israeli ambassador to the U.S., said Israel “isn’t anxious to launch military action.”

“It doesn’t want this, but Israel thinks more should be done and that diplomacy alone isn’t enough. I think Israel and the U.S. are on the same page but on different sides of the paper,” he said.